1. Field of the Invention
The present invention relates to a switch device used for detecting, for example, a shifted state of a transmission, an operational state of a brake or the like in a vehicle, and a method for sealing the connected portions of lead wires of the switch device.
2. Description of the Prior Art
A conventional switch device used for detecting a brake, a back gear or the like in a vehicle is disclosed, for example, in Japanese Utility Model Publication No. 22492/92.
In the prior art switch device of this type, an operating element is inserted from outside through an opening into a tightly closed switch chamber in which a switch is accommodated, and a flexible sealing member penetrated by the operating element seals the opening. The switching operation of the switch is carried out by cooperation of an urging of the operating element with a resilient force of a spring. If an external force is applied to an outer end of the operating element, the operating element is retreated to operate the switch. The operating element repeats its advancing and retreating movements every time the switching operation of the switch is carried out.
In the prior art switch device, however, an inner peripheral edge of a through-hole in the sealing member is merely fit in an annular groove which is formed around an outer periphery of the operating element. Therefore, the fitted portion of the sealing member may be stripped off and slipped off from the annular groove, resulting in incorrect sealing of the device. Particularly, when the switch device is used for detection of the shifted state of the transmission of the vehicle, a problem occurs if such strip-off or slip-off of the sealing member occurs because transmission oil can enter the switch chamber hindering the switching operation.
To insure a switching accuracy for a long period of time, it is required that the operating element is always operated accurately along a predetermined path. In the prior art switch device, however, the following problem is encountered. A guide means for assisting the accurate operation of the operating element is not provided for the operating element. Particularly, an inner end of the operating element is in a free state and for this reason, the operating element may fall down or be deflected during operation thereof, thereby reducing the accuracy of the switching operation, resulting in a non-reliable device.
In addition, in the switch device of this type, the amount of displacement of a portion to be detected differs depending on what is being detected such as detection of the shifted state of the transmission or detection of the operational state of the brake. Therefore, it is necessary to change the detection stroke depending upon the place where the switch device is used. Thus, in the prior art, a plurality of the switch devices are prepared in correspondence to the different amounts of displacement of the portion to be detected, which results in an increased cost.
When a connection terminal of the switch device is to be connected to a lead wire, the connected portion of the switch device is disposed on a bottom of a recess defined in a casing. After connecting the lead wire, a filler is poured into the recess to seal the connected portion from the outside. This creates a problem because a periphery of the recess makes the connecting operation difficult resulting in a degraded operatability or resulting in a connection failure.